My '52 starts well when cold but after running for 15 to 20 minutes and turning it off, the starter cranks very slowly. This true even when I have put a good charge on the battery. If I let it cool off for an hour it cranks right up. The battery is in a separate compartment under the flat bed behind the cab with a long run of battery cables to the ground and starter. I think I will try to replace those and see if that is a quick fix. It is 12 volt conversion for most of the electrical circuits if that makes any difference. Any ideas on where I can look for answers?

 

I might be tempted to point you in a different direction. What does your engine temperature look like when you say it's "warmed up." Is it possible it's getting "HOT" when it sits and thus binding a little? -- And after you wait a bit it has cooled down a bit, right???? I'd take a look at my engine temps and possibly my oil pressure to ensure the engine is getting the oil it needs between parts when hot as well.

It could also be combining with that long cable to weaken the cranking. Long cables - not great!....36" max unless it's a big around as a hogs leg (2 inch).

Try it with the battery out of the back of the truck and close to the engine with shorter cables hooked up

J!

 

Just a guess but I'd bet it's the cables. You say they are long runs. Have you upgraded the size of the cables. Do the cables get hot when cranking. Ground battery close to frame, make sure engine has ground strap to frame. Make sure all connections are clean and tight. Use a piece of welding cable for the positive cable, large diameter.

 

Just a question, did this start after the battery relocation? I've had a starter play games with me before when the engine got warm, it would turn over slowly. Replaced my starter and problem went away.
Good luck, a balmy -7 this morning here in Alberta...

 

I would do as mentioned above, make sure you have good, clean cable connections. If all is good there I would suspect the starter. One problem that develops is the bushings in the end caps of the starter wear out. There is very little clearance between the armature and fields in the starter, when the starter gets warm the armature expands and the worn bushings allow the armature to come into contact with the fields. If you allow the starter to cool the armature will contract and again you will have clearance. The starter will work like this for a while until the bushings completely wear out.

 

In addition to above. Many older trucks and cars put their batteries in the back, so don't give up. Is your battery fairly new and high cranking amps? I've seen many shops that do fittings on battery cables, do a terrible job on connections. Make sure the cables are of the correct size. Correct size bolts to attach cables to frame etc. I've seen small bolts used and they don't provide enough metal to metal contact or tight enough. Solenoids are just relays and over time they start arcing, check it. have a great day, chuck

 

My cyber space wild guess is……….starter.
(rent, borrow or steal a hand help starter draw gauge?)


"but being wrong keeps me humble"

 

I would guess it's the starter also for the reasons Bob mentioned. Whtever it is, it is obviously heat related.

Where are your coil and ballast resistor located? If they are both remote from the engine (firewall, fender, etc.), then fine. However, if one or both are mounted to the engine (like at the front of a head), the heat buildup will cause them to be weak at a hot restart. Don't ask how I know this!

 

I agree with your comment as far as resistor is concerned, but generally speaking, coil was always mounted on front of head, at least on flatheads. you want air blowing on coil to keep it cool, and as long as coil is on bracket off head, no issue!

 

RJ, how do you know that?? OOH. sorry...